recent advancements, trends and future paradigms in structural design...

Recent Advancements, Trends and Future Paradigms

in Structural Design of Reinforced Concrete (RC) Tall

Buildings

Naveed Anwar, PhD

Why new paradigms and needed?

Concrete Asia 2016 Naveed Anwar, AIT 3

How long do we have

before the building will

collapse din this fire?

- Asks the Fire Chief from the structural

engineer / (Architect)

1974

Concrete Asia 2016 Naveed Anwar, AIT

The Towering Inferno (1974)

4

https://www.youtube.com/watch?v=FagbC09BO2o


The Challenges

• Architectural Design and Structural Engineering

• Bigger, taller, complex forms, but

Lighter, smaller, thinner structural elements

• High performance, but Lower cost

• Architects and Structural Engineers

• Apparent lack of innovativeness

• Difficulties in collaborative working

5


Percentage of Urbanized World

6


World’s Population Urban-to-Rural Ratio

7

(www.un.org)


Urbanization →Growing Needs for built-up space


The Case of London


Advise to my fellow Engineers

1. Design is a team effort, and Architect is the lead

2. Everything is possible, don’t say no!

• but it needs innovation, knowledge, skills, tools and,

• of course resources

3. - - -


Conceptualizing a Solution

• Design a Rectangular Water Tank of

3mx4mx2m

−Most engineers will readily calculate the

wall thickness and required rebars and the

cost

11

• Design the most efficient and cost effective

water tank to hold 24 cuM of water

−Many designs are possible

−Most engineers will not know how to start?


A tussle between Heuristic and the Rational

12

Should design be based on

“Engineering Judgment” and

intuition,

Or

controlled by explicit computations

and, restrictive limits and rational

approaches


It is by logic we prove, but by intuition we

discover


Intuitive/Artistic Creations – Need no codes

14

Structural systems: Meeting new architectural demands


Conventional Systems


Development of Basic Structural Systems

17


Intuitive design, verification, application

18

Félix Candela


Intuitive forms and designs

19

Pier Luigi Nervi


The Diagrid System

21


BRB Based Systems (Braces that Don’t Buckle)

22


Innovative Systems

23

Doha Tower, QatarCTBUH best Tall Building Award 2012

KfW Westarkade, FrankfurtCTBUH best Tall Building Award 2011


Mercury City Tower in Moscow – The Tallest

building of Europe

Sky City (Changsha, China)Burj Khalifa, Dubai


Innovative Systems

25

Linked Hybrid, BeijingCTBUH best Tall Building Award 2009

Shanghai World Financial Center, ChinaCTBUH Award 2008

The Beetham Hilton Tower, Manchester, UK, CTBUH Award 2007


Construction Innovations: Pre-Fabrication

26


Construction Innovations: Slip Forming

27


Construction Innovations: Top Down Construction

28


Construction Innovations: Modular Construction – 30 story in 15 days - China

29


Construction Innovations: Concrete Printing

30


Construction Innovations: Contour Crafting

31


The Growing Computational Requirements: Progressive Collapse

• A new and major concern for structural safety

• Structure should not collapse completely if one or two elements are “destroyed”

• Backup systems, alternate load paths, additional redundancy


Analysing for Construction Sequence

• Structure is normally analysed as if it is already fully built

• Make the model, and apply loads

• Step-wise construction sequence analysis is essential for better and correct understating and

design

• Make the model, as it is built

• Apply loads as they are applied

• Consider temporary shoring etc

• Consider in-construction corrections

• Consider the aging effects


Without and With Construction Sequence

34


Innovative Solutions

• Connecting two buildings or parts of structure in the right way can lead to innovative solutions

• Rigidly connected

• Fully free to move

• Flexible connections

• Elasto-Plastic Connections

• Fuses

Design approaches: Looking beyond Life Safety


Evolution of our Understanding of Structures

Limits on the allowable stresses to achieve in-direct FOS

Explicit consideration of partial FOS.

Formulation of limit state design principles.

Formulation of ultimate strength.

The recognition of the difference between brittle and ductile failure.

The introduction of capacity based design approaches.

Performance based design and more explicit linkage between demand and performance.

Risk integrated based design, and a more and holistic approach towards consequence based engineering.


Seismic Design Approaches

Code Based Design

Performance Based Seismic Design

Consequences and Risk Based Design

Resilience Based Design


The First Building Code: Code of Hammurabi (1792 BC to 1750 BC)

39

Clause 229:

If a builder builds a house for someone, and does not construct it

properly, and the house which he built falls in and kills its owner,

then that builder shall be put to death.


Ancient Building Code: Laws of Moses

40

“In case you build a newhouse, you must also makea parapet for your roof, thatyou may not place bloodguiltupon your house becausesomeone falling might fallfrom it”.

- The Bible, Book of Deuteronomy, Chapter 22, Verse 8


Development of Buildings Codes

41

“Rebuilding of London

Act” after the “Great Fire of

London” in 1666 AD.

In 1680 AD, “The Laws of

the Indies” Spani

sh Crown

London Building Act of

1844.

In USA, the City

of Baltimorefirst building code in 1859.

In 1904, a Handbook of the Baltimore

City

In 1908 , a formal

building code was

drafted and adopted.

The International

Building Code (IBC) by (ICC).

European Union,

the Eurocodes.


The Modern Codes

42

(ACI 318 – 11)

Extremely Detailed prescriptions and

equations using seemingly arbitrary, rounded limits with

implicit meaning

(IS 456-2000)


The General Code Families

43

UBC, IBC

ACI, PCI, CRSI, ASCE, AISI,

AASHTO

British, CP and BS

Euro-codesChina, USSR,

Japan


Are All Buildings Codes Correct ?

• If they differ, can all of them be correct ?

• Did we inform the structures to follow which code when earthquake strikes ?

• Codes change every 3 or years, should be upgrade our structures every 3 or 5 years to conform

?

44


45

Is my Structure safe?

What level of Richter earthquake my structure sustain?


Prescriptive Codes – A Shelter

• Public:

• Is my structure safe ?

• Structural Engineer:

•Not sure, but I did follow the “Code”

As long as engineers follow the code, they can be

sheltered by its provisions

46


Shortcomings of Code Based Design

• Traditional codes govern design of general, normal buildings

Over 95% buildings are covered, which are less than about 50 m

• Not specifically developed for tall buildings > 50 m tall

• Prescriptive in nature, no explicit check on outcome

• Permit a limited number of structural systems

• Do not include framing systems appropriate for high-rise

• Based on elastic methods of analysis

• Enforce uniform detailing rules on all members

• Enforce unreasonable demand distribution rules

• Do not take advantage of recent computing tools


Design for Seismic Resistance and Extreme Events

• Force/stress based design

• Assume reduced forces, limit the stresses

• Displacement based design

• Allow force D/C to exceed, as long as displacements can be limited

• Capacity based design

• Put “fuses” in the structure limit the force capacity, hence the demand

• Energy based design

• Total energy input is collectively resisted by kinetic energy, the elastic strain energy and energy dissipated

through plastic deformations and damping

48


Implicit Intent of Code Based Design

• Resist small shocks through stiffness and no damage

• Resist moderate earthquakes through strength with some damage

• Respond to strong earthquakes through damping, ductility and enrgy dissipation without collapse,

but significant damage


Progression of Seismic Resistance Design

50

Historical Approach:Earthquake forces proportional tobuilding mass (Vdes = 5 - 10% of Wt),

Traditional Codes:Elastic earthquake forces reduced forlinear design (Vdes = Vmax /R)

Lack of Knowledge on Earthquake Demand and

Building Capacity

Linear Elastic Building Response

V

Vdes

Yield Max

V

Vdes

Elastic Forces reduced for Design by R

Inelastic Response


Current Seismic Design Approach

51

Current Trend:a) Inelastic earthquake demand based

on, inelastic capacity of buildingb) Resolution of demand vs. capacity

generates Performance Pointc) Design based on displacement, ∆des

des Sd

Performance Point

Demand Reduced Based on Inelastic Capacity of

Building


Ductile link Analogy for Capacity based design

52

C. V. R. Murty, 2002



Code Based Design





Performance Based Design (PBD)

• An approach in which structural design criteria are expressed in terms of

achieving a set of performance objectives or levels.

• Ensures structures reaches specified demands level in both service and

strength design levels.

• Why it was needed?

• Traditional codes not suitable/adequate

• Explicit verification not specified or required in most codes

• Public does not care about the code, or theories or procedures, they care about

“safety” and ‘performance”

54


Prescriptive Vs Performance

55

Approach Procedure Outcome

Prescriptive(emphasis on procedures)

Specify “what, and how to do”

Make Concrete: 1:2:4

Implicit Expectation

(a strength of 21 MPA is expected)

Performance Based Approach(emphasis on KPI)

What ever it takes

(within certain bounds)

Explicit Performance

Concrete less than 21 MPA is rejected


Define Performance Levels

56

Based on FEMA 451 B


Link the Damage to Performance Levels

57

Structural Displacement

Lo

adin

g S

ever

ity

Resta

urant

Resta

urant

Resta

uran

t

Ha

zard

Vulnerability

Consequences


Link Performance other Indicators

58

Restaurant Restaurant

Resta

uran

t

Operational (O) Immediate Occupancy (IO) Life Safety (LS) Collapse Prevention (CP)

0 % Damage or Loss 99 %

Ref: FEMA 451 B

CasualtiesLowest Highest

Rehab Cost to Restore after eventLowest Highest

Retrofit Cost to Minimize ConsequencesHighest Lowest

Downtime for RehabLowest Highest


How to Work with PBD

59

Requires:• Detailed modeling• Nonlinear-dynamic analysis• Appropriate computing tools, knowledge , skills

and lots of patience

Go Beyond Codes

Sophisticated Structural Modelling

Stare of Art Computer

based tools


Performance Based Design Process

Analyzing Linear Elastic Model

for Code Based Design Loading

Formulation & Analysis of

Nonlinear Model of Real Building

Results Extractions and

Processing

Interpretation of Results for

Decision Making


AIT’s Focus on PBD

• Considerable research, development focus on

PBD

• Specially targeted to Tall Buildings and

retrofitting of exiting structures

61


Park Terraces Tower 1 Podium, Philippines

The Sequoia , Philippines

GSIS, Philippines

LDCC, Nepal

La Residenza, Thailand

Gramercy, Philippines Serendra , Philippines


Beyond PBD

• For public, the performance criteria

still does reduce the effects of the

events

• Insurance companies want to have

greater reliability of assessment of

risk and damages

63



Code Based Design





Questions still un-answered

• What if the chance that performance level is not achieved?

• What is the risk ?

• What are the consequences?

• What if the performance levels are not sufficient?

Code based was implicit, with not confirmation of response

PBD is explicit, can help to confirm the response and

performance level


Is this acceptable?Even though it satisfies CBD and PBD


Why do we need to go Beyond PBD

• For public and society, the performance criteria still does reduce the effects of the events

• The non structural damage is not acceptable

• The disruption and loss goes much beyond the building

• Insurance companies want to have greater reliability of assessment of risk and damages


Consequence Based Engineering

• It is not enough to say “Cracking and non-structural damage is acceptable, as long as structure

does not collapse”

• A natural extension of the performance-based design approach

• Structural consequences can be defined in terms of repair costs, casualties and loss of use

duration (dollars, deaths and downtime) (Porter, 2003).

• Other types of consequences which result from the inherent function of a structure, are addressed

using importance factors for various occupancy categories in design codes (Yuxian 2013).

68


Consequence Based Engineering

• “Structural consequence and non-structural effects” determined entirely from the analysis of

structural member as well as overall system behavior.

• The consequence-based structural design approach proceeds through the analysis of expected

system consequences, irrespective of the event triggering these consequences.

• This philosophy requires the structural members to be designed for variable reliability levels,

depending upon their contribution in causing adverse system consequences.

69


Risk Based Design Process

Safety Studies (Probability and

Consequence Analysis)

Risk Quantification

Safety Critical Element

Design Accidental

Load

Structure Design


Parameters of Risk Based Seismic Assessment

Site Seismic Hazard

Likelihood of Failure

(Structure Vulnerability)

Consequence of Failure

Pro

bab

ility

of H

azard

Expected Consequences

Acceptable Risk Limit

Higher Priority

Lower Priority

Risk Plot (High and Low Priorities)


Special Purposes Guidelines from USA

72

Applied Technology

Council (ATC)

Federal Emergency Management Agency

(FEMA) and

National Earthquake

Hazards Reduction Program (NEHRP)

PEER Guidelines

for Tall Buildings

Tall Buildings Initiatives

(TBI)

CTBUH Guidelines



Code Based Design





RESILIENCE

Economic

Social

Organizational

Technical

Resourcefulness

Redundancy

Rapiditty

Robustness

Lower

Consequences

Faster

Recovery

More Reliability

4 Dimensions of

Resilience

4 Properties of

Resilience

3 Results of Resilience

74


Resilience Based Earthquake Design

• A holistic approach which seeks to identify all

earthquake-induced risks (including those outside the

building envelope) and mitigate them using integrated

multi-disciplinary design and contingency planning to

achieve swift recovery objectives in the aftermath of a

major earthquake.

• The key principle in resilience-based earthquake

design is to limit expected damage to structural and

architectural components and egress systems

(elevators, stairs, and doors)

75

Economic Loses

Loss of Community and Culture

Loss of Quality of

Life

Go Beyond Life Safety


Green Buildings Resilient Buildings

76

Main authors : ArupSupported by USRC and many others


Enhancement of Structural Design

Code Minimum

Requirements

Design Demands

Vertical Earthquakes

Minimum Structural Damage

Minimize Residual

Drift

Expose Structural Elements

Symmetric Design

Source: REDiTM Rating System

77

Tools: How to design efficiently?


The Role of Computers and Software

79

• Initially, computers were used to program

the procedure we had

• Now, we develop procedures that are suited

for computing


Design Approaches evolved to match computing revolution

80


Some Tools of the Trade

81

Integrated 3D Bridge Design Software

Integrated Software for Structural Analysis and Design

Integrated Analysis, Design and Drafting of Building Systems

Integrated Design of Flat Slabs, Foundation Mats and Spread Footings

Nonlinear Analysis and Performance Assessment for 3D Structures

Design of Simple and Complex Reinforced Concrete Columns

By Computers and Structures Inc. USA


Decisions Support Systems

• Explicit learning from experience

• Combination of Rational and Heuristic thinking

• Encapsulating natural thinking process into formal decision systems


A Swing Towards the AI

• Rich Pictures

• Analytical Hierarchy Process (AHP)

• Artificial Neural Networks (ANN)

• Genetic Algorithms (GA)

• Expert Systems (ES)

• Fuzzy Logic

• Deep Thinking

• Big Data and Data Mining

83


Rich Picture for Choosing Structural System


ANN for Tall Buildings

85

Architectural Layout

Preliminary SizingStructural Response

• Number of story• Length, Width,

Height• Grid spacing• ..

• Column size• Shear wall size• Rebar quantities

• Natural period• Drift ratio• Base shear

To make design preliminary decisions without explicit calculations


Mobile computing might change how we design

86


Can we make it safe ?

87

Control: Making structures smarter


Smart Everything !

•Smart Phone

Smart Car

Smart TV

Smart Home

Smart City


Why smart structures ?

• Excitation fluctuates so Demand fluctuates

• But Capacity is constant

• Therefore level of safety is not consistent

• Typically capacity is designed based on “Peak” estimated demand

• What if peak demand never comes > Un-economical

• What if demand exceeds estimated peak > Un-safe


What a smart structure does?

ability to sense any change in external actions

diagnose any problem at critical locations

measure and process data

take appropriate actions to improve system performance while preserving structural integrity, safety, and serviceability

1

2

3

4


Smart structures use smart devices and materials to add

some intelligence to adapt, react, adjust, respond and

handle multiple demands, and levels as and when needed

Help to make the structures safer, specially for earthquakes

and strong winds


Smart Structure Devices

Energy Dissipating

Systems

Active or Passive Control

Systems

Health Monitoring

Systems

Data Acquisition

System


Applications for Smart Structure Devices

Structures subjected to extraordinary vibrations

Important structures with critical functionality and high safety requirements

Flexible structures with high serviceability requirements

1

2

3


Research Areas in Smart Structure Technology

• Analytical or numerical modeling of control systems.

• Experimental investigation of control systems

• Properties of smart materials and their applications

• Applicability and Full-scale implementation

• Development of guidelines and standards for design of smart systems


Damping Devices and Systems

Damping devices and systems applied to a lateral load-resisting system


Damping Devices and Systems

Passive Control Systems

Semi-active Control Systems

Active Control Systems

Hybrid Systems


Passive Control Systems

• Use Various mechanical devices which reacts to structural vibrations resulting in dissipating a

portion of their kinetic energy.

• Requires no external power source and are capable of generating large damping forces with

increasing structural response


(a) (b) (c)

Tuned Mass Dampers (TMD)

Direction of Vibration

P

(a) (b)

Tuned Liquid Dampers (TLD)


Beam

Co

lum

n

Brace

Friction

Damper

Hinges

Links

Moment

Connections to

Braces

Friction Damper

Slotted Slip

Joints

Friction Devices


Beam

Co

lum

n

Brace

Yielding

Damper

Rods

Rod Rings

Yielding Damper

Metallic Yielding Devices


Tuned Mass Dampers (TMD) Tuned Liquid Dampers (TLD)


Viscoelastic Dampers

Brace

VE

Damper

Pinned Connections

Fluid Viscous Dampers


Common Semi-active Control Systems

Semi-active Tuned Mass Dampers

Semi-active Tuned Liquid Dampers

Semi-active Friction Dampers

Semi-active Vibration Absorbers

Electrorheological Dampers

Semi-active Stiffness Control Devices

Magnetorheological Dampers

Semi-active Viscous Fluid Damper


Active Control Systems

Use electrohydraulic actuators which generate optimum amount of control force based on actual measured response of main structure

Effective Control on Structure Response

Adaptability to Ground Motion Characteristics

Suitability to Use for any

Control Objectives

Ability to Suppress

Responses Against Wide

Range of Frequencies

Advantages


Active Mass Dampers (AMD)

Comparison of Smart Structures with AMD and TMD Model & Free Body Diagram for Structures with AMD


α

x(t)

ẍg (t)u(t)

Active

tendon

Actuator

Active Tendon System Active Bracing System with Hydraulic Actuator

Active Mass Dampers (AMD)


Hybrid Mass Damper Hybrid system with base isolation and actuators

Common Hybrid Systems

Hybrid Damper Actuator Bracing Control


Intelligent Hybrid Control Systems

Working Mechanism of Three Stage Intelligent Hybrid System

Structure

> Ist Threshold

Structure

> 2nd

Threshold

Structure

Damper Damper Actuator Damper Actuator

Ground Motion

Stage 1 Stage 2 Stage 3

Response Response

NoYesNo Yes

Will Adjusted feedback gain


Base Isolation Systems for Seismic Response Control

Tend to reduce the energy transfer from ground acceleration to structure.

Bearing

Elastomeric Bearings

Sliding Type Bearings

Most Important Component


Common Types of Bearing

Elastomeric Bearings Lead-Plug Bearings

Piston with Teflon-Coated

Surface at the topElastomer Base Pot

Seal

Top Plate with Stainless Surface

Typical Plot Type Bearing


Types of Bearing

Friction Pendulum Bearing Friction Pendulum Bearing with Double Concave


Sensing and Data Acquisition Systems

Sensors

Actuator(s)

Amplifier

Filter

Multiplexer

Signal Conditioner

A/D

Observer

Controller

D/A

Data

Recorder

Display

Smart Structure

Control Computer

Components of Data Acquisition and Digital Control Systems

Thank you

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